1. Field
The present innovations relate to solar cells, and, more particularly, to thin-film solar cells having contacts on the backside, only.
2. Description of Related Information
Solar cells may be characterized by their electrical contacts, such as those with electrical contacts on both the front side and backside of crystalline silicon solar cells. With regard to solar cells, the front is generally considered to be the side from which the sunlight enters the device. In existing devices, the n-doped region (cathode) and p-doped region (anode) are arranged in a vertical manner, front side to backside, and separated by a lightly doped region.
In addition to other drawbacks, solar cells with front-side contacts suffer from “shadowing”, i.e., shadows caused by front side structures that diminish the sunlight that reaches the solar cell to be transformed into electricity. To avoid this problem, existing solar cell fabrication methods sometimes use transparent conductive oxides (TCOs) for front-side contacts. One such transparent conductive oxide is ITO (Indium-Tin-Oxide). Notably, the use of these transparent electrodes involves a trade-off between electrical and optical performance, i.e., a thicker layer will have lower resistance and hence a higher electrical efficiency. However, a thicker layer will also transmit less light into the solar cell and hence create lower optical efficiency. Furthermore, TCO/ITO layers are also very sensitive to moisture an contribute to the degradation of solar cell efficiency and reliability over their 20-30 year lifetime. In addition, backside contact solar cells generally require high quality device layers (e.g. silicon) which have not yet been possible given existing technologies.
With regard to solar cells consisting of crystalline silicon, most devices are formed with front and backside contacts. However, some limited technologies for such full-silicon substrates do utilize contacts on the backside, only. One drawback of these technologies is that they generally require high temperature anneal processes (e.g. 900° C.) to passivate the backside and also to diffuse the dopants into the silicon substrate. Such high temperatures are above the softening point of glass and cannot be used with thin film technologies that utilize glass and plastic substrates. In addition, the purely silicon substrates require a thickness of more than 150 or 200 μm for mechanical stability. This increases the material costs substantially as well as the processing/manufacturing costs, e.g., due to the need for high temperature steps, etc.
As set forth below, one or more exemplary aspects of the present inventions may overcome such drawbacks and/or otherwise impart innovations consistent with the systems and methods herein via the provision of backside only contact thin-film solar cells and/or devices.